Sokil\Mongo\Operator::increment PHP Method

    public function increment($fieldName, $value = 1)
    {
        // check if update operations already added
        $oldIncrementValue = $this->get('$inc', $fieldName);
        if ($oldIncrementValue) {
            $value = $oldIncrementValue + $value;
        }
        $this->operators['$inc'][$fieldName] = $value;
        return $this;
    }